quote:ScienceDaily (Jan. 7, 2010) — The discovery of fossil footprints from early backboned land animals in Poland leads to the sensational conclusion that our ancestors left the water at least 18 million years earlier than previously thought.

The results of the Polish-Swedish collaboration are published online in the journal Nature.ScienceDaily (Jan. 7, 2010) — The discovery of fossil footprints from early backboned land animals in Poland leads to the sensational conclusion that our ancestors left the water at least 18 million years earlier than previously thought.

For nearly eighty years, palaeontologists have been scouring the planet for fossil bones and skeletons of the earliest land vertebrates or "tetrapods" -- the ultimate progenitors of all later amphibians, reptiles, birds and mammals including ourselves. Their discoveries have suggested that the first tetrapods evolved relatively rapidly from lobe-finned fishes, through a short-lived intermediate stage represented by "elpistostegids" such as Tiktaalik, about 380 million years ago. But there is another potential source of information about the earliest tetrapods: the fossilized footprints they left behind.

In the new study a Polish-Swedish team describe a rich and securely dated footprint locality from Zachelmie Quarry in Poland that pushes back the origin of tetrapods a full 18 million years beyond the earliest skeletal evidence and forces a dramatic reassessment of the transition from water to land.

The trackways show that large tetrapods, up to three metres in length, inhabited the marine intertidal zone during the early Middle Devonian some 395 million years ago.